The present invention relates to power stoppage minimizing systems for distribution lines and methods of using the distribution lines, and more particularly to a power stoppage minimizing system for a distribution line and a method of using the distribution line which minimize a power stoppage section and power stoppage time when a short-circuit accident occurs in the distribution line.
A disconnection of a distribution line is another possible accident that can be handled, by maintaining healthy sections under supply of power, and by specifying and cutting away the disconnection section as in the power stoppage minimizing system which copes with the short circuit.
Conventionally, the distribution line is used such that an accident occurring in the distribution line is removed in a time-limit sequential feed protective system which is disclosed, for example, in "COMPREHENSIVE POWER SUPPLY TECHNIQUE MANUAL", published by Ohm, Nov. 30, 1991, pp. 464-465.
That system is provided with a section switch, a time-limit sequential feed unit and a power supply transformer at each section point on the distribution line. When an accident occurs on the distribution line, a protective relay installed in a substation is operated to interrupt a circuit breaker connected to a distribution bus to open the switch connected to the distribution line that has zero voltage, and then re-closes the circuit breaker. This causes the switch on the distribution line at a position nearest the circuit breaker to be impressed with a voltage to thereby be re-closed. This causes the next switch to be impressed with a voltage to thereby be re-closed. This operation is iterated until the end switch is re-closed. When an accident occurring on the distribution line is of a recoverable type, the opening of the circuit breaker eliminates the accident and the operation continues thereafter. If the accident is of a permanent type where a short circuit continues due to breakage of devices connected to the distribution line, the circuit breaker is re-opened and power is thereafter supplied up to the switch at the position of occurrence of that accident and no power is supplied to the subsequent line and devices. In such a case, the normal state of the system is recovered by eliminating the cause of the accident manually.
The problem with the conventional time-limit sequential feed protective system, as just mentioned above, is that a power stoppage of about 30-60 seconds occurs due to the opening of the circuit breaker. The recent spread of computer systems does not permit the occurrence of a power stoppage in the distribution line, so that a distribution line power stoppage minimizing system is desired which minimizes a power stoppage section and power stoppage time.
Although minimization of the power stoppage section and time is naturally required also in the case of a short circuit accident, the progress of a deterioration in the power supply equipment including distribution lines, switches, transformers, etc., of the distribution equipment due to stresses, that is, due to a rise in the temperature of those devices caused by the flow of an overcurrent through those devices is great in the case of a short circuit accident in the distribution line. Thus, the power stoppage time permitted from the occurrence of an accident to its elimination is about 0.2 seconds and other power stoppage sections must not exist in the distribution line.